convert OpenEXR float to color value
The values are scene referred.

You require a view transform to map to the display referred range.

If you choose to use the sub-optimal sRGB EOTF, you are losing a heck of a lot of dynamic range. You can use a much wider dynamic range for the scene referred to display referred transform if you wish. Ultimately it is always a creative decision.

See Render with a wider dynamic range in cycles to produce photorealistic looking images for more information.